There are no general methods to solve PDEs exactly.

Most of the time you apply heuristics and/or chose an efficient numerical algorithm (= try-and-error approximation in plain language)

Numerical approximations mean a lot of number crunching, which are hardly done in Python or Perl.

The book is most likely addressing external libraries in C or Fortran which interface with Python.

The heuristic (aka symbolic calculation) parts OTOH can be translated to Perl, if implemented in pure Python.

IIRC this kind of stuff used to be done in MATLAB or similar tools.